A search was conducted in the U.S. Patent and Trademark Office on the subject matter of this application. The search resulted in the citation of the following U.S. Pat. Nos. 3,116,157; 3,356,513; 3,376,247; 3,541,589; 3,926,656; and 4,177,230. While I believe that none of the cited patents teach or suggest the method that I claim in this application. I will discuss each of the cited patents hereinbelow.
U.S. Pat. No. 3,116,157 issued on Dec. 31, 1963, for a "Refractory Ramming Mix." This patent discloses that a polymer is added to a ramming mix and the polymer added must have silicon and oxygen in its composition in order to decompose to form a SiO.sub.2 refractory bond. The polymers used in this patent are used in conjunction with organic solvents such as toluene, not with water, which is the common vehicle used in forming casting slips for a slip casting operation. Also, it is important to note, this patent is not related to a slip casting operation and is not in any manner instructive in the art of casting slips containing silicon metal particles.
U.S. Pat. No. 3,356,513 issued on Dec. 5, 1967, for "Production of Silicon Oxynitride." This patent shows some slip casting of Si.sub.2 N.sub.2 O with polymer additives. A low molecular weight anionic polymer deflocculant (less than 1,000 molecular weight) is used optionally with a high molecular anionic polymer vehicle thickener (molecular weight being greater than 50,000).
U.S. Pat. No. 3,376,247 issued on Apr. 2, 1968, for a "Slip Casting Composition with Cyclopentadiene as a Deflocculant". This patent discloses the use of high amounts (5-12% by weight) of a polymer of molecular weight less than 300 in a nonaqueous vehicle for slip casting. There is no mention in this patent of slip casting of silicon articles.
U.S. Pat. No. 3,541,589 issued on Nov. 17, 1970, for a "Process for Preparing Silicon Nitride Coated Refractory Material." This patent relates to a B.sub.4 C-Si.sub.3 N.sub.4 composite for use in coating other refractories. The patent does not discuss slip casting of material and in particular does not discuss the slip casting of a silicon metal containing slip.
U.S. Pat. No. 3,926,656 issued Dec. 16, 1975 for an "Improved Flow Molding Composition." This patent is directed to an injection molding system, not to a slip casting system.
U.S. Pat. No. 4,177,230 issued on Dec. 4, 1979, for a "Process for Producing Reaction Sintered Silicon Nitride of Increased Density." This patent is directed to an impregnation process for reaction bonded silicon nitride, not to a forming process such as slip casting of silicon which is subsequently nitrided.
Additional prior art that I am aware of which was not cited in the search on this subject matter includes U.S. Pat. Nos. 4,217,320 and 4,301,020. Also included is an article from the Journal of Colloid and Interface Science, Vol. 55, No. 1, April, 1976, entitled "The Role of Polyelectrolyte Charge Density and Molecular Weight on the Adsorption and Flocculation of Colloidial Silica with Polyethylenimine" by Lindquist et al.
U.S. Pat. No. 4,217,320 issued on Aug. 12, 1980, for a "Slip Cast Article Manufacturing Method." This patent is cited simply to show what a slip casting system is.
U.S. Pat. No. 4,301,020 issued on Nov. 17, 1981, for a "Process of Slurrying and Spray Drying Ceramic Oxides with Polyethyleneimine Dispersants." This patent is cited because it is the only example known to me of the use of a very high molecular weight polyethyleneimine polymer in any ceramic processing. The process disclosed in this patent, however, is a spray drying process not a slip casting process. Also, the process is used in the manufacture of ferrites and not in the manufacture of articles from silicon metal powder.
The Lindquist et al article is one in which a polyethylenimine (PEI)-water-Ludox AM colloid silica system was used as a model system to investigate the relationship of charge density and molecular weight of polyelectrolyte on the adsorption and subsequent flocculation of oppositely charged colloid particles.